Keying monitor



Feb l2, 1945' A. A. WALSH ETAL 2,394,573

KEYING MONITOR Filed Dec. 9. 1943A :FACIL WAHM/free 25 ATTORN EY Patented Feb. 12, L

AKEYING MoNrroa Allen A. Walsh," West Englewood, N. UJ., and Wilbur C. Besides, New York, N. Y., assgnors to Radio lCorporation y Delaware 4 Application Decemb In telegraph systems it is desirable to haveat the transmitter means for'aurally monitoring the keyed wave being transmitted.

The manual keying of a radio telegraph transmitter can in most instances be improved for. the

operator if some means are available for monitoring the keyed signals.

The generalobject of this invention isto improve aural monitoring of telegraph signals. Heretoiorehtwo general methods vhave been employed. In one of these methods oscillations from a heterodyne oscillator aremixed with a signal from the radio frequency section of the transmitter to provide an aural beat note which may be observed. The .other method involves use of an audio oscillator which' is actuated by the key and does notmake use ,of the heterodyne principle. f

A more detailed object of this invention is to provide an improved aural monitor ci.l the second type described above, wherein anaudio'oscillator is actuated by the key and heterodyning oscillations are unnecessary.

A still further object of this invention is to provide monitoring means for use in light weight compact telegraph systems operating on batteries or other perishable power supplies.

A still further object of this invention is to provide a simpliied light weight monitor which requires extremely little operating power, the required power in fact being so small that it is practically negligible and may be disregarded when considering the power supply for the transmitter.

The above objects and others which will appear in the description which follows, are attained by providing a simple relaxation type oscillator employing a gaseous tube such as a small neon tube connected with an RC network and keyed as the transmitter is keyed. The values of R and C of the network are chosen so as to produce the desired audio frequency. The wave generated, which is of audible frequency, is applied to some type of transducer for observation, for example, a telephone head set.

A feature of the invention resides in the compactness of the monitor, the simplicity thereof, as well as in the small amount of power required to operate the same. This is of considerable importance where the transmitter and monitor must be of small dimensions and of light weight for portable use.

In describing our invention more in detail refof America, a corporation oi fr 9,1943, seriallNo. 5132500 4 claims, I(ci, 250517.)

arrangement associated with a transmitter-,alim accordance with our invention.

In Fig. 1,v t the left, is shown a transmitter of a simple type comprising a source of oscillations l0, a nal amplifier stagev including a tube l2 having its grid and cathode excited by oscillations from source I0 and its anode coupled with a tank circuit I4, in turn 4coupled with' utilizing means such as, for example, radiating means. It should be noted that bias for the control grid can be supplied by any of theV conventional methods, for example, by a leak resistance I6, while the remaining electrodes, except the cathode, is supplied by operating potentials froma single source. The transmitter is keyed by lmanipulating the key 20 in the direct current supply lead to the anode and screen grid of tube l2. Other types of transmitters may be used, provided they include a ldirect current keying circuit.

The monitor all of which is included in the dotted rectangular 26 comprises a', gaseous tube 30 having its electrodes shunted by a condenser C, with the tubes anode and condenser C coupled by resistance R to th'e direct current circuit completed by key 20 in operation. Transducer means, such as a telephone head set 34, is coupled to the monitor by a condenser C l In operation when the key 20 is closed, to signal, condenser C is charged through resistance R. When the charge on C reaches a critical value the tube 30 breaks down and changes from a high impedance to a low impedance and conducts. Oscillations are thereby generatedA of a frequency depending on the rate at which C is charged through resistance R to the said critical value and discharged by the tube 30. This rate in turn depends on the values of R and C.

The choice of values of R and C will depend upon two conditions, first, the voltage required to operate the gas tube, and second, the desired audio monitor frequency. The condenser Cl is made large enough to provide suflicient coupling of the generated oscillations to th'e transducer 34. The wave form of a relaxation oscillator of this type is a saw tooth, but since it is used only for monitoring, it is found to be perfectly satisfactory.

In the modification in Fig. 2, the keying monitor is used as described above' and serves an additional purpose which will now be described.v

The terminal at which .the transmitter is located usually includes a radio receiver and the two may be used alternately to communicate to other somewhat similar stations. The receiver may beof any desired type and has not been shown in detail. It will, however, include an output tube 40 having its anode coupled to a transducer andin accordancewith our invention thetransducer may serve in the monitor so that the anode of the tube 46 is coupled by condenser 46 Vto the transducer 3d. Now when the transmitter key 29 isin ,thevup position, thatlianon-operative, the gas tube 3U remains coupled :for faudible quencies, across the receiver output. When the receiver output level reaches a value such as :to

break down the gas tube 30, the impedance there- Y ofk becomes low. In this manner a peak limiting actionv is obtained and this action is of considerable value in reducing disturbing noises 'such as? `static, etc. v The stage il'in the receiver wherein the peak limiting is accomplished, may have a resistivecapacitive output as showna't I46, orfatr-an'sformer output :48. In the latter case, the connectonlis made as shown in dotted lines. In the latter case, if/he tube 30 may be coi'mected across kthe :secondary Winding of the {transformer-A8.

addi-tional '.beneiift `derived from the-:use ofr Y our monitor Vlx-'esides in gthe fact fthat since R .and

the battery operated apparatus is thus 1assured.

Moreover, .the monitor requires Ya 4small space ttor installation.

radio frequency stage Yvvhereinrradlo frequency energy is relayed, and a source of direct current potential is connected to said stage by a key, a

monitor comprising a tube having electrodes coupled in a circuit'for the production of oscillations of tone frequency when direct current potential 1ci proper value `is,suppliedsto-the@said `circuit, a :couilirrg :including saidllzeywhen closed rbetween said circuit and said source, and a transduce #coupled to said oscillation producing circuit.

2. In combination with a transmitter having a nlrari-io frequency stage wherein radio frequency wenergyis relayed, .and a source of potential is connected to ,said stage by any known modulation method suchas a key, a monitor comprisingl a relaxation Loscillator including a tube having electrodes, a' condenser coupledto said electrodes, 'a lchargingresistance foi-*said condenser coupling saidicondenserthrough said key when closed to said source, and a transducer coupled tothe os- ;cillator. l v l In .combination fa `signalling system, 'a lradio frequency stage wherein radio #frequency energy Vsfrelayed, and-a source .o potential isY Vpionnier:ted to 'said-"stage by :ako-y or its equivalent,

land ra circuit wherein :curfrenlts representing jaudible signals appear, an :aural-monitor #compris-V v-in-g arolaxation oscillator including faftube hav- Y ,ing fflectrodes, ;a Ycondenser `icou-pled fto fsaid elecisn and 1is about V1 finch long :and 1/4 :inch -infdiame'ten li410 "R -andf'C and C I -'arealso very small. We claim: v

il. In combination with a transmitter having a trades, ea coupling including :a charging imped- :ancie vandsaid-.lneywhenclosed coupling said-con- :denser to esaid suurce, :and a transducer coupled -tofthe oscillator andan said-circuit wherein fsaid #currents representing ysignals appear, the `'arrangementbeingzsnch that-Whenthe fkey is v.closed f -zoscillations :are generated in .said 'itube for monitoringemnrposes, and when #the .zkey is open said tube acts as a peak limiter for the currentsnsaid Alast mentioned circuit.'

Y 4, n @combi-nationfasaecitedan siam-2, wherein said xzondensers dn :shunt the tnbeel'ectrodes Y ic, Rasmus. 

